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Posted by Graham Relf at 11:51 on 2013 Dec 20
Yes, I do have a flat box (cardboard box lined with white paper, 4 torch bulbs in the corners next to the circular aperture that goes over my telescope). I still do not often use it. I agree that it’s a simple way to fix vignetting but I tend to do that in post-processing (various methods).I would certainly use my flat box if I had any optics between my telescope and the camera body (to magnify the target*) because there is then a risk of out-of-focus dust spots and rings which a flat frame would correct.(* or perhaps a coma corrector but again I have one but don’t use it because I found it introduces other problems such as ghosting from bright stars – the coma is not conspicuous in my Horsehead photo). I think the golden rule (as in software development) is to keep things as simple as possible.
Posted by Grant Privett at 09:36 on 2013 Dec 20
Yes, I know what you mean about the dithering provided by a mount’s PEC (and/or slight non-alignment) reducing noise – I used a Super Polaris for some years and found that after 50 or so frames the background could be very smooth indeed.RE: flats I wasnt thinking of photometry – it can be done with a DSLR, but its not the obvious choice. The main advantage of a flat in this instance is in reducing obvious vignetting. I feel dark corners in images detract from the overall appearance – especially with extended targets.It doesnt take long to create a flat (I put a plain fairly opaque plastic bag over the end of my ‘scope and point it at a nearby evenly illuminated wall) and with some scenes the resulting image is greatly improved. Not essential, but often worth it if you have the time.
Posted by Nick James at 00:08 on 2013 Dec 20
Just cleared here and Gaia is exactly where GaiaontheSky says it should be at around mag 10.3 so an easy target.I’ve uploaded a timelapse to Youtube:Timelapse video of Gaia
Posted by Graham Relf at 09:49 on 2013 Dec 19
Grant, A good question. I did NO flats or darks. I rarely do.This is another thing which I think puts beginners off. Yes, you must do those things for photometry but otherwise there is no need (with today’s cameras – and mine is 5 years old now). I know this attitude will be controversial.My method takes into account the inevitable fact that the unguided mount is inaccurate. That makes the camera’s fixed pattern noise and defective pixels wander around among the sequence of star images. So when they are stacked those problems are watered down by a factor equal to the reciprocal of the number of exposures taken. I find that is sufficient – except when doing photometry.Of course the mount must not be so inaccurate that a star image is elongated by more than the radius caused by atmospheric turbulence. That determines the maximum length of each exposure. My HEQ5 fits the bill fine for exposures of half a minute and sometimes 1 minute. In suburbia you cannot do exposures as long as that at high sensitivity anyway without complete fogging. (But the Horsehead cannot be photographed from suburbia because it is below the background level. I have tried.)
Posted by Grant Privett at 22:14 on 2013 Dec 18
Thanks for that. Will settle down with a beer and watch those at the weekend.Certainly saves the train journey to London.
Posted by Grant Privett at 22:13 on 2013 Dec 18
Could you tell us whether you dark subtracted and flat-fielded please?
Posted by Charles Taylor at 18:25 on 2013 Dec 17
Many thanks for the superb image – you have inspired me to take courage and have a bash with my fairly basic DSLR (Olympus E410) and my 200mm Newtonian over the Christmas holidays. By then, if Santa is kind, my EQ5 should be motorised.
Posted by Phillip Hudson at 13:25 on 2013 Dec 17
Really nice picture and very encouraging to see it done with kit as you describe
Posted by Nick James at 10:32 on 2013 Dec 15
Thanks. It’s good to know that these recordings are appreciated.We had an excellent Christmas meeting yesterday and I hope to have recordings uploaded soon.Nick.
Posted by TonyAngel at 20:13 on 2013 Dec 14
Quite agree. Lucie Green has proved her self in the community and if there has to be another professional she would be the best.I suspect that BBC is doing to Sky at Night what C4 did to Time Team.
Posted by Steve Holmes2 at 16:53 on 2013 Dec 14
She would indeed have been an excellent choice. Superb CV, currently active in astronomy research, interest in science education, passionate to engage the public with space science and astronomy (note!), recipient of an award for excellence in public engagement with science, very pleasant unassuming TV manner, clearly knowledgeable about her subject and interested in those of others …. and one could go on.Problem is, she’s not a "media personality", is she? Yes, I know this is actually greatly to her advantage and would make her a much more appropriate presenter than Dr A-P, but maybe the BBC don’t see things that way. Also, we’re all assuming that the present team in fact want to carry on. It could well be that they were recruited on a strictly temporary basis and are now keen to return to their "day jobs".Of the other presenters, while Chris Lintott seems to have established himself quite happily I’m not sure Messrs Abel and Lawrence could carry the programme effectively in the long term so there’s clearly a need for someone else to at least share the helm. But for goodness sake, even if Lucie Green is not willing to be that person surely there has to be someone better than Dr A-P??Suggestions, anyone?Steve Holmes
Posted by D A Dunn at 10:30 on 2013 Dec 14
As a member living in France, can I second the comment as to the usefulness of being able to access the meeting videos on line. Well done the BAA.David
Posted by Charles Taylor at 10:13 on 2013 Dec 14
As a new member of the BAA and one unlikely to visit London – I live in the wildernesses of Perthshire – can I say how much I am gaining from this service. In particular, I enjoyed listening to Prof Leatherbarrow’s ‘Now and Then’ Presidential Address and look forward to delving into other videos as time allows.Many thanks for this privision – Graham Taylor
Posted by Steve Holmes2 at 18:08 on 2013 Dec 13
If only she was an "expert" perhaps it wouldn’t be such an issue! Frankly, I feel she has already had the benefit of any doubt I would wish to give her, following the debacle of "DWRNTM" and her other decidedly dumbed-down presentations.Yes, she has been involved in many branches of science but this was many years ago. Her tribology thesis was 1995 and she seems to have done her "hands-on" work developing instruments for satellites in the early 2000’s. There’s then a big gap in her Wikipedia career profile before the "she is now working on and managing" phrase so I guess she’s now more a manager than a scientist as such. She probably currently spends a lot more time "communicating" than researching/developing, in any case. All of which is fine, but there is no "astronomical" qualification there at all! Yes, she may have "wanted to be an astronaut" as a child (didn’t we all?) but even she says she is "committed to inspiring new generations of astronauts, engineers and scientists" – no mention of astronomers there! – and always describes herself as a "space scientist". This lack of an astronomical background (and presumably knowledge base) does not bode well. Her emphasis on children and young people is also worrying: while ‘The Sky At Night’ must of course continue to attract an ongoing audience it is not (and was never intended to be) a "children’s programme". To try to make it so would clearly invite disaster.Her credits are said to include the mini-series ‘Paradox’ (panned by the critics and cancelled after one series); ‘Dr Who Confidential’ (just one appearance, and that as a "space scientist"); the infamous DWRNTM (no further comment needed!), and ‘How Satellites Rule Our World’ (2012): not an impressive list. I think I saw the last one and was not impressed by the level of its content – definitely one for the masses rather than a serious study. Example – when discussing geostationary orbits, did we get an explanation based on the fact that higher orbits take longer to traverse and hence if you go high enough it will take 24hrs = geostationary? No, we got the presenter running round a carousel, trying to keep up with it as it turned and saying you had to go a long way out as "gravity was so weak there" you wouldn’t be pulled back to the earth. Oh dear!As for inviting lots of people with different skills to tell us about their work (as per Sir Patrick’s approach) I have this nasty feeling that Dr A-P will not be able to keep herself in the background long enough for much useful to be said! (as Sir P was very adept at doing). Not sure how much respect such (real) experts would have for a "science populariser" in any case: will they even agree to appear?I fervently hope that our fears for the programme will not be realised but I’m not at all confident. Recruiting Dr A-P and moving to BBC4 may sound the death-knell for TSAN, not herald its salvation – but maybe that’s what the BBC are intending all along??Steve Holmes
Posted by TonyAngel at 18:58 on 2013 Dec 12
Ok Richard I will give it a try. I have to say that I am against "experts" being parachuted in when there are enough people on the ground who have won their spurs many times over. To move away from an Amateur Chairing the programme is quite drastic.
Posted by Richard Miles at 11:11 on 2013 Dec 12
The analogy of the cat amongst the pigeons springs to mind. I see that her Wikipedia profile ias already up to date following the announcement in yesterday’s Guardian that she will be the new S@N TV host (alongside Chris Lintott). See:http://www.theguardian.com/media/2013/dec/11/maggie-aderin-pocock-sky-at-nightTony – I certainly would give her the benefit of the doubt. I do not know her personally and so am wont not to prejudge the matter. The BBC were never going to have a mad-keen amateur fronting up the show, and so long as they invite lots of amateurs with lots of different skills and experiences to participate, then it should work out. Interesting that during the early 1990’s she got involved in another branch of science (tribology) so she may be a good choice for someone who is able to bring together folk from across a variety of disciplines which might help reach new viewers and widen the scope of the programme.Richard
Posted by TonyAngel at 09:30 on 2013 Dec 12
I cannot believe it. Maggie Aderin-Pocock is going to be joint running Sky at Night!!!!!!!!!!!!!!!!!!!!!!!!!! There are at least a dozen top BAA members who are more suited.One viewer lost. 🙁
Posted by Richard Miles at 18:24 on 2013 Dec 09
Just one final point, Eliot. You write:"Using a bigger aperture or a more sensitive camera will only decrease the time to which you get to the sky’s limiting magnitude (however shorter exposures are useful for faster moving objects)."The sky will have a certain brightness (usually in the range for a dark sky of magnitude 19.5-21.5 per square arcsecond – V mag equivalent). So imagine the seeing and sky brightness are fixed then the bigger the aperture, the greater the signal to noise and so the fainter the limiting magnitude. N.B. The plate limiting magnitude is often stated to be an SNR of 2.5.If my memory serves me correctly, the faintest object I have reported astrometry of using a Celestron 11 is V=21.5. I stacked quite a few images for that!Cheers,Richard
Posted by Grant Privett at 16:37 on 2013 Dec 08
Sounds about right. When detection is what you seek, Newtonians are better than refractors – as they bring all colours to focus at the same point and ensure you collect as many photons as you can.It is true that detecting objects that are just 1% brighter than the surrounding sky signal is difficult, but with care (good flats, clean optics, using the best dark nights only, many exposures) good results can be achieved. It has the added advantage that, having mastered the imaging of the very dim, you will have refined your techniques and will find your imaging of brighter targets also improves.Either way, its fun.
